Work units such as walk-behind trenchers typically include a frame having a front end and a back end. A working element (e.g., a trenching boom, an excavating blade, or other type of attachment) is located at the front end of the frame and an operator station is located at the back end of the frame. A power source such as an internal combustion engine is mounted on the frame. The power source provides power to a drive arrangement such as a hydraulic drive. The hydraulic drive can drive components of the working element at the front of the frame, and can also drive propulsion elements (e.g., tires, tracks, or other traction structures suitable for propelling the working device over the ground) positioned at left and right sides of the frame.
Some prior art work units of the type described above are adapted to be manually steered. One example of a manually steered work unit is the RT 100 Walk-behind Trencher sold by Vermeer Manufacturing. This type of unit has elongated leveraging arms/handles that project rearwardly from the frame of the work unit. During use, the operator stands between the arms and uses the arms to manually steer the work unit. However, work units can often be quite heavy, awkward and difficult to maneuver. Therefore, the effectiveness of a manual steering system is often dependent on the size and strength of the operator.
Automatic steering systems for work units have also been developed (e.g., see U.S. Pat. No. 7,059,434). These types of steering systems can include a pivotal steering and propulsion control handle provided on a dash or control panel located at the rear of the work unit. While existing automatic steering systems are not dependent on the size and strength of the operator, they can have other shortcomings. For example, they may not allow the operator's hand to be positioned in a comfortable or ergonomic position during operation of the unit, or may also not be intuitive to use. Furthermore, such steering systems do not allow an operator to use both hands to grasp leveraging arms during forward or reverse movement of the work unit.
What is needed is a work unit with an improved control system such as an improved power steering system.